The present application is based on and claims priority from the following Japanese Patent Applications: 2001-78726, filed Mar. 19, 2001; and 2001-232461, filed Jul. 31, 2001; the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a DC motor that has an armature core comprised of an inner core and an outer core and an armature coil wound around a bobbin.
2. Description of the Related Art
An armature of a conventional DC motor is comprised of an armature core and an armature coil that is inserted into a plurality of slots to be wound around teeth of the armature core so that an end of each phase coil is welded to commutator segments of a commutator.
In the above armature, because each phase coil has to be inserted into one of the slots from the opening between the teeth, the space factor of the armature winding relative to the space of the slots is limited to a low value.
In addition, because the coil end is welded directly to the commutator, it is difficult to change connection of the phase coils, for example from series connection to parallel connection, or from star connection to delta connection, when the armature coil is mounted into the armature core.
Therefore, the present invention has been made in view of the above problems.
It is a main object of the invention to provide a DC motor that has a high space factor of the armature coil of the DC motor relative to the space of the slots of the armature core thereof.
Another object of the invention is to provide a DC motor that is easy to change connection of the armature coil.
According to a preferred embodiment of the invention, a DC motor includes an armature core that is comprised of an internal core unit and an external core unit coaxially disposed outside the core unit, a plurality of bobbin-and-armature-coil sets respectively mounted on teeth of the armature core, a case having a plurality of first terminal members respectively connected to commutator segments and the armature coils in a prescribed connection pattern.
Therefore, it is not necessary to directly wind the armature coils around the armature core, so that the space factor of the armature coil can be increased. In addition, because of the first terminal member, the connection of the armature winding can be changed easily only by changing the connection pattern of the first terminal member.
It is preferable that the first terminal members are integrated with the commutator.
It is also preferable that each of the bobbins includes a second terminal member that is coupled to one of the first terminal members. The armature coil wound around each bobbin is connected to the second terminal member, so that the connection of the armature coils can be easily carried out.
It is also preferable that each pair of the first terminal member and said second terminal member forms a male-female coupler. Therefore, reliable connection of the armature coils can be ensured.
The external core unit may be comprised of a plurality of circumferentially separated external cores each of which has one of the teeth and one of the bobbins.
In the DC motor, the bobbin may have a brim portion that fills up a gap between adjacent external cores, the external cores and said internal core unit may be connected to each other by projection-concavity connection.
It is also possible that each of the external cores has a dovetail projection, and that the internal core unit has a plurality of dovetail concavities each of which is fitted to the dovetail projection.